Fuel injection valve and a method for operating the same

ABSTRACT

A fuel injector ( 1 ), especially an injector for fuel injection systems of internal combustion engines, includes a first solenoid coil ( 5 ), which cooperates with the first armature ( 9 ), a valve needle ( 13 ) in a force-locking connection with the first armature ( 9 ) for actuating a valve-closure member ( 14 ), which together with a valve seat surface ( 15 ) forms a sealing seat, and a second solenoid coil ( 6 ). In this context, the first armature ( 9 ) is acted upon in a closing direction by a first resetting spring ( 11 ). A second armature ( 10 ) cooperates with the second solenoid coil ( 6 ) such that, when the first solenoid coil ( 5 ) and the second solenoid coil ( 6 ) are supplied with current, a limit stop body ( 18 ) that is connected with the valve needle ( 13 ) strikes against the second armature ( 10 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a fuel injector according to thespecies of claim 1, and to a method according to the species of claim 9,for the actuation of a fuel injector.

[0002] The closing times of fuel injectors are lengthened, on the onehand, by the adhesion forces between the armature and the core and, onthe other hand, by eddy currents. To decrease the delay, it is known tocause a current to flow through the solenoid coil in the reversedirection in response to ending the current pulse that excites the fuelinjector, in order to accelerate the decay of the residual field.Designing appropriate control elements is difficult and also yields onlyslight improvements in the closing times.

[0003] Another possibility is seen in building up one magnetic field foropening the fuel injector and building up a second magnetic field tohold the fuel injector in its open position. The strength of the holdingfield can then be selected so as to be so small that the eddy currentsare small after the holding field is switched off.

[0004] From German Patent 23 06 007 C3, an electromagneticallyactuatable fuel injector is known for injecting fuel into an internalcombustion engine, in which the solenoid coil has three windings, whichare driven by three separate circuits. In this context, the firstcircuit acts to rapidly open the fuel injector, the second circuit tokeep the fuel injector open, and the third to generate a demagnetizingfield that extinguishes the residual magnetic field, for rapidly closingthe fuel injector.

[0005] One disadvantage in the fuel injector known from German Patent 2306 007 C3 is that it is very expensive to manufacture an arrangementthat has three circuits, which drive the three windings of the solenoidcoil.

[0006] In addition, the spray-discharged fuel quantity per time unit isalways identical, so that the metering of smaller fuel quantities in thelower rotational speed range of the internal combustion engine must berealized through a significantly shortened closing time and thereforethrough more powerful resetting springs and necessarily increased driveoutputs of the solenoid coils. This places stress on the electricalcomponents.

ADVANTAGES OF THE INVENTION

[0007] In contrast, the fuel injector according to the present inventionhaving the features of claim 1, and the method according to the presentinvention having the features of claim 9, have the advantage that themetered fuel quantity per time unit can be switched over as a functionof the rotational speed, because two switch positions are available,which can be driven individually in a selective manner, as a result ofthe alternating supply of current to two solenoid coils that cooperatewith two armatures.

[0008] In this context, one advantage for the opening dynamics isespecially the installation of a limit stop body, which, depending onthe supply of current to the solenoid coils, either takes the secondarmature with it in the opening direction or strikes against the secondanchor that is held fixed in place.

[0009] As a result of the measures indicated in the subclaims,advantageous refinements and improvements of the fuel injector describedin claim 1 are possible.

[0010] Especially advantageous are the high closing dynamics, caused bythe active switching back of the fuel injector from the opened to theclosed state, the closing dynamics making possible very short closingtimes from both switch positions.

[0011] As a consequence of the closely-fitting dimensioning of the twoworking gaps, the fuel injector can achieve the desired injectionproperties for each switch position.

[0012] The first switch position having a small cross-sectional openingis especially advantageous in the lower rotational speed range, becausesmall fuel quantities can be metered.

[0013] Also advantageous is the possibility of being able to switch fromthe lower switch position directly to the upper switch position.

DRAWING

[0014] One exemplary embodiment of the present invention is depicted insimplified form in the drawing and is discussed in greater detail in thedescription below. The following are the contents:

[0015]FIG. 1 depicts an exemplary embodiment of a fuel injectoraccording to the present invention in a cutaway representation and

[0016]FIG. 2 depicts a diagram of the current-supply state of thesolenoid coils for the switch positions of the exemplary embodiment ofthe fuel injector according to the present invention depicted in FIG. 1,as well as the corresponding stroke of the valve needle as a function oftime.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0017]FIG. 1 in a partial cutaway representation shows thespray-discharge-side part of a fuel injector 1. Fuel injector 1 isparticularly well suited for the direct injection of fuel into acombustion chamber, not depicted further, of a mixture-compressing,spark-ignition internal combustion engine.

[0018] Fuel injector 1 includes a core 2 and a nozzle body 3, which aresurrounded by a valve housing 4. A first solenoid coil 5 and a secondsolenoid coil 6 are arranged on valve housing 4 and are surrounded by afirst magnetic backflow body 7 and a second magnetic backflow body 8,respectively. Arranged between core 2 and nozzle body 3 are a firstarmature 9 and a second armature 10, which cooperate with solenoid coils5 and 6. First armature 9 is acted upon in the closing direction by afirst resetting spring 11, whereas second armature 10, in the idle stateof fuel injector 1, rests on nozzle body 3. Clamped between firstarmature 9 and second armature 10 is a second resetting spring 12, whichacts upon second armature 10 in the closing direction. The spring forceof first resetting spring 11 is significantly greater than the springforce of second resetting spring 12.

[0019] Connected to first armature 9 is a valve needle 13, which at itsspray-discharge-side end has a valve-closure member 14. Valve-closuremember 14, together with a valve seat surface 15, forms a sealing seatand is held in a sealing position on valve seat surface 15 of a valveseat body 16 by first resetting spring 11. At least one spray-dischargeopening 17 is configured in valve seat body 16.

[0020] A sleeve-shaped limit stop body 18 is mounted on valve needle 13in a form-locking manner. A first working gap 19 is created betweenfirst armature 9 and core 2. A second working gap 20 is created betweensecond armature 10 and limit stop body 18. In this context, firstworking gap 19 is larger than second working gap 20.

[0021] The fuel is conveyed to the sealing seat via a central fuelsupply 23 and fuel channels 21 a, 21 b in armatures 9 and 10, as well asthrough a central cut out 22 of nozzle body 3.

[0022] If an excitation current is applied to first solenoid coil 5,first armature 9 moves in the opening direction along with valve needle13, connected to it. Valve-closure member 14 lifts off from valve seatsurface 15. If second solenoid coil 6 remains without current supply,then first armature 9 traverses one stroke, which corresponds to theaxial extension of first working gap 19. In this context, first armature9 moves in the opening direction along with valve needle 13 and limitstop body 18, mounted thereon, until limit stop body 18 strikes againstsecond armature 10. Since second armature 10 can be displaced againstthe force of second resetting spring 12, the armature is moved in theopening direction as a result of the motion of valve needle 13 via limitstop body 18. After the closing of first working gap 19, an upper switchposition is reached. The fuel is spray-discharged into the combustionchamber via spray-discharge opening 17.

[0023] At lower rotational speeds of the internal combustion engine,fuel injector 1 is not opened to the upper switch position, but only toa lower switch position. The stroke path then corresponds to the axialsize of second working gap 20. For this purpose, second solenoid coil 6is first supplied with current. This causes second armature 10 to beheld in position on nozzle body 3. If first solenoid coil 5 is nowsupplied with current, then first armature 9, along with valve needle13, mounted thereon, moves in the opening direction until limit stopbody 18 strikes against second armature 10. Because second solenoid coil6 is supplied with current and holds second armature on nozzle body 3,fuel injector 1 is only opened to the lower switch position. In thismanner, a smaller quantity of fuel can be metered, which in addition hasa different jet spray property, e.g., a different angle distribution.

[0024] To close fuel injector 1 from the upper switch position, bothsolenoid coils 5 and 6 are supplied with current. If the current,exciting first solenoid coil 5, is switched off, both the force of firstresetting spring 11 as well as the magnetic force of second solenoidcoil 6 act in the closing direction. Fuel injector 1 in this manner isactively switched from the opened to the closed state.

[0025] If the excitation current of first solenoid coil 5 is switchedoff, first armature 9, along with valve needle 13 connected thereto, aswell as second armature 10, are accelerated from the upper switchposition in the closing direction, as a result of the resetting force offirst resetting spring 11, in that the magnetic force of second solenoidcoil 6 actively pulls second armature 10 in the closing direction. As aresult of the cooperation of the various forces and the fact that firstresetting spring 11 needs only to accelerate first armature 9 and avalve needle 13 in the closing direction, but not second armature 10,short closing times are achieved.

[0026] The closing of fuel injector 1 from the lower switch positionalso occurs by switching off the current that excites first solenoidcoil 5. Because second armature 10 on nozzle body 3 is held in positionby current-supplied second solenoid coil 6, only first armature 9, alongwith valve needle 13, has to be accelerated in the closing direction.Here the resetting force of first resetting spring 11 causes the closingof fuel injector 1. As a result of the small stroke, valve-closuremember 14 is rapidly put back into the starting position, which alsoresults in short closing times.

[0027] To illustrate the switching processes, FIG. 2 depicts thecurrent-supplied and non-current-supplied states of first solenoid coil5 and of second solenoid coil 6, in connection with a diagram whichshows valve stroke h as a function of time t. The electrical currentthrough first solenoid coil 5 is designated as I₁, and the electricalcurrent through second solenoid coil 6 as I₂. In the lower rotationalspeed range of the internal combustion engine, when only a small fuelquantity is metered, fuel injector 1 is switched to the lower switchposition. For this purpose, second solenoid coil 6, which holds secondarmature 10 on nozzle body 3, is initially supplied with current. As aresult, when first solenoid coil 5 is supplied with current, firstarmature 9, along with valve needle 13 mounted thereon, is only liftedto the point that limit stop body 18 strikes against second armature 10.The closing of fuel injector 1 from the lower switch position isperformed by switching off current I₁, which excites first solenoid coil5 (diagram left).

[0028] If the upper switch position is to be driven, second solenoidcoil 6 remains unsupplied with current, whereas first solenoid coil 5 isexcited. As a result, first armature 9 lifts valve needle 13 to thepoint that first armature 9 strikes against core 2 and first working gap19 is closed. To terminate the opening process, second solenoid coil 6is also supplied with current. However, first armature 9, along withvalve needle 13 mounted thereon, is still held on core 2. If current I₁,which excites first solenoid coil 5, is now switched off, then themagnetic field of first solenoid coil 5 is eliminated, and firstarmature 9 falls away from core 2. First armature 9 is switched back tothe closing position by the resetting force of first resetting spring 11and by the magnetic force of second solenoid coil 6. The closing processcan therefore proceed significantly more rapidly, because, in additionto the resetting force of first resetting spring 11, the magnetic forceof second solenoid coil 6 is also available for the closing process(diagram right).

[0029] If fuel injector 1 is first to be switched to lower switchposition and then to the upper switch position, solenoid coils 5 and 6are supplied with current in the following manner: first, secondsolenoid coil 6 is excited, to hold second armature 10 on nozzle body 3.If first solenoid coil 5 is now supplied with current, first armature 9,along with valve needle 13, is moved in the stroke direction until limitstop body 18 strikes against second armature 10. Thus the first, stableswitch position is reached. First solenoid coil 5 and second solenoidcoil 6 are supplied with current. To switch from the lower, first switchposition to the upper, second switch position, current I₂, which excitessecond solenoid coil 6, is switched off. In this manner, the magneticfield that holds second armature 10 on nozzle body 3 is removed, thusmaking it possible for first armature 9, taking with it second armature10, to be further pulled into the magnetic field of first solenoid coil5, until first working gap 19 is closed. If the upper switch position isreached, then only first solenoid coil 5 is supplied with current.

[0030] To close fuel injector 1, second solenoid coil 6 is once againsupplied with current. After a satisfactory build-up of the magneticfield of second solenoid coil 6, first solenoid coil 5 is switched off.As a result, fuel injector 1 returns to the initial position (diagramcenter).

[0031] The present invention is not limited to the exemplary embodimentdepicted and can also be realized in a multiplicity of other designs offuel injectors 1.

What is claimed is:
 1. A fuel injector (1), especially an injector forfuel-injection systems of internal combustion engines, having a firstsolenoid coil (5), which cooperates with a first armature (9), a valveneedle (13) in a force-locking connection with the first armature (9)for actuating a valve-closure member (14), which, together with a valveseat surface (15), forms a sealing seat, and a second solenoid coil (6),the first armature (9) being acted upon in the closing direction by afirst resetting spring (11), wherein a second armature (10) cooperateswith the second solenoid coil (6), such that, when the first solenoidcoil (5) and the second solenoid coil (6) are supplied with current, alimit stop body (18), connected to the valve needle (13), strikesagainst the second armature (10).
 2. The fuel injector as recited inclaim 1, wherein a second resetting spring (12), clamped between thefirst armature (9) and the second armature (10), acts upon the secondarmature (10) in the closing direction.
 3. The fuel injector as recitedin claim 1 or 2, wherein the spring force of the second resetting spring(12) is substantially smaller than the spring force of the firstresetting spring (11).
 4. The fuel injector as recited in one of claims1 through 3, wherein between a core (2) and the first armature (9) isconfigured a first working gap (19), and between the limit stop body(18) and a second armature (10) is configured a second working gap (20),the first working gap (19) being larger than the second working gap(20).
 5. The fuel injector as recited in claim 4, wherein the fuelinjector (1) can be switched to a first switch position having a firstcross-sectional opening by closing the second working gap (20) as aconsequence of supplying current to the first solenoid coil (5) and tothe second solenoid coil (6).
 6. The fuel injector as recited in claim5, wherein the fuel injector (1) can be switched to a second switchposition, having a second cross-sectional opening by closing the firstworking gap (19) as a consequence of supplying current to the firstsolenoid coil (5) only.
 7. The fuel injector as recited in claim 5 and6, wherein the first cross-sectional opening is smaller than the secondcross-sectional opening.
 8. The fuel injector as recited in one ofclaims 4 through 7, wherein the fuel injector (1) in the second switchposition spray-discharges a fuel jet, whose jet image is different fromthe jet image of the fuel jet spray-discharged in the first switchposition.
 9. A method for actuating a fuel injector (1), especially aninjector for fuel-injection systems of internal combustion engines,having a first solenoid coil (5), which cooperates with a first armature(9), a valve needle (13) in a force-locking connection with the firstarmature (9) for actuating a valve-closure member (14), which, togetherwith a valve seat surface (15), forms a sealing seat, and having asecond solenoid coil (6), the first armature (9) being acted upon in theclosing direction by a first resetting spring (11) and by a secondarmature (10), which cooperates with the second solenoid coil (6), suchthat, when the first solenoid coil (5) and the second solenoid coil (6)are supplied with current, a limit stop body (18) connected to the valveneedle (13) strikes against the second armature (10), having thefollowing method steps: switching the fuel injector (1) to a firstswitch position having a first cross-sectional opening by supplyingcurrent jointly to the first solenoid coil (5) and to the secondsolenoid coil (6), or switching the fuel injector (1) to a second switchposition having a second cross-sectional opening that is larger than thefirst cross-sectional opening by supplying current only to the firstsolenoid coil (5).
 10. The method as recited in claim 9, wherein thefuel injector (1) is switched to the second switch position from thefirst switch position by switching off the current exciting the secondsolenoid coil (6).
 11. The method as recited in claim 9 or 10, whereinthe fuel injector (1) is switched from the second switch position to aclosing position by supplying current to the second solenoid coil (6),operating in the closing direction, and by switching off the currentexciting the first solenoid coil (5).